The present invention relates to a ring spinning machine and, more particularly, to an improvement in the construction of a ring spinning machine of, the type which is suited to high-speed operation and which has a direct drive spindle which is driven directly by an electric motor.
A ring spinning machine has been known which has a direct drive spindle (referred to simply as "spindle" hereinafter) which is driven directly by an electric motor. The spindle has a ring for guiding a yarn to be wound on the spindle and a ring rail for supporting the ring and is constructed such that the lower end of the range through which the ring and the ring rail move is positioned above the motor structure of the spindle. This type of spindle is disclosed, for example, in Japanese Patent Examined Publication No. 54-32864 and Japanese Patent Unexamined Publication Nos. 49-20445 and 58-109633.
Such spindles are required to operate at a high speed to comply with a demand for higher production efficiency in yarn spinning process. Unfortunately, however, the spindle of the conventional construction could not sufficiently meet this requirement because the rotation speed of the spindle is limited due to the presence of a resonance speed in primary flexural mode which appears between the upper free end of the spindle and the portion of the spindle held by an upper bearing in a bolster which supports the spindle.